1. Field of the Invention
This invention relates to the preparation of hydrocarbon conversion catalysts, and particularly to an improved economical process for preparing a zeolite containing hydrocarbon cracking catalyst containing a synthetic inorganic matrix wherein the level of ammonium salt pollutants in air and water is reduced.
2. Description of Prior Art
Generally, the most common process for preparing zeolite promoted hydrocarbon conversion catalyst is incorporating the crystalline aluminosilicate zeolite into an aqueous inorganic matrix containing, e.g. silica, alumina, silica-alumina and/or clay. Thus, according to some methods crystalline zeolites can be dispersed in a suitable siliceous sol and the sol can be gelled by various methods. Other procedures involve the addition of the crystalline zeolite to a gelatinous precipitate of silica-alumina or amorphous silica alumina hydrogel and spray drying of the admixture to form spheroidal composite particles containing zeolite crystals embedded in the silica-alumina matrix. Even though the processes for forming the amorphous silica-alumina matrix material may vary, generally, a pH control and neutralization step is required in the formation of the silica-alumina gel which involves the addition of an ammoniacal base e.g. ammonium hydroxide prior to the filtration of the composite. Commercial processes employing the latter ammonium hydroxide addition step present significant pollution problems attributed to the presence of high levels of ammonium ion reagents. In the conventional procedure, in which ammonia is used prior to primary filtration, part of the ammonium ions end up in the plant effluent, creating a water pollution problem. Ammonia is also released by the catalyst into the atmosphere during spray-drying, thus creating an air pollution problem.
As a result of this invention, it has been found that highly active, attrition resistant and stable zeolite containing hydrocarbon conversion catalysts containing amorphous silica-alumina matrices can be prepared by an economical and improved process which reduces the level of polluting ammonium salts in the plant effluent and eliminates air pollution by ammonia during the conventional spray-drying process.